PSG Lite

This crate generates PCM waveforms similar to those of the AY-3-8910 and its compatible chips. This crate is not intended for high-quality audio applications. The main use case is generating simple sound effects and tones in resource- constrained environments. It is designed with a focus on speed to be usable on 8-bit CPUs (such as AVR¹). Emulating the chip is not the goal. As such, there are significant differences from the AY-3-8910 in terms of functionality.

• Hardware Envelope: Not implemented. Channel volume ranges from 0 to 15.
• Noise Generator: The number of bits in the shift register differs. Specifically, it is 16 bits instead of 17 bits.
• Tone Period: 0 cannot be set. The minimum value is constrained by the clock rate and sample rate.

Sample Rate

PSG has an extremely simple structure, but the upper limit of the frequency that can be generated is 125KHz at a clock rate of 2MHz. This crate reduces processing load by simply thinning out waveforms without performing downsampling. Therefore, at low sample rates, especially in the high-frequency range, the sound quality deteriorates significantly. At a sample rate of around 48000Hz, the sound quality is generally acceptable. If a sample rate of 250KHz is specified, waveforms are generated with almost no degradation.

In a PC environment, most audio frameworks automatically perform sample rate conversion before outputting to the device. Therefore, it is often possible to play back a sample rate of 250KHz without any issues.

Features

This crate has the following features flags:

float: Enables generating samples in f32 format. Enabled by default. If this flag is not set, floating-point operations are not performed.

Usage

To use this crate, create a SoundGenerator instance, configure the tone period and mode for the channels, and then generate samples. The interface is simple and designed for use in embedded systems. Below is a basic example.

use psg_lite::{SoundGenerator, Output};

fn main() {
    const CLOCK_RATE: u32 = 2_000_000;
    const SAMPLE_RATE: u32 = 48_000;

    let mut generator = SoundGenerator::new(CLOCK_RATE, SAMPLE_RATE);

    generator.set_mode(0, Output::TONE);
    generator.set_volume(0, 15);
    generator.set_period(0, 123);

    for _ in 0..SAMPLE_RATE {
        let sample: i16 = generator.next_sample();
        // Process the sample (e.g., send to DAC or audio buffer)
    }
}

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT) at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Footnotes

1. Although the C++ implementation (same structure) worked on ATTiny, it has not been confirmed with Rust. ↩